Reinforcing cage for an armored concrete element

ABSTRACT

The invention relates to a reinforcing cage for a concrete element ( 1 ) comprising at least two layers of longitudinal armorings (C, T) maintained spaced from one another by transverse armorings (E).  
     According to the invention, each longitudinal armoring of a layer is composed of a metal flat bar ( 3, 3′ ) parallel to the corresponding face of the element ( 1 ) and whose width and thickness are determined in relation to the loads applied in order to form, as transverse section, the necessary area to provide the required strength, and the transverse armorings ( 4 ) for maintaining the spacing between two layers are welded to the opposite internal faces ( 31, 31′ ) of both longitudinal flat bars ( 3, 3′ ) so that the global thickness of the cage ( 2 ) does not exceed the spacing between their external faces, whereby the thickness (H 2 ) of the molded element ( 1 ) is reduced accordingly.

[0001] The invention relates to a reinforcing cage for an element madeof armoured concrete and also covers concrete elements comprising such acage.

[0002] The invention relates especially to the realisation ofprefabricated elements of armoured concrete.

[0003] In the field of construction and civil engineering, constructionelements made of moulded concrete in which a metal armouring isimbedded, have been used for a long time.

[0004] It is known that the principle of armoured concrete consists incombining the qualities of concrete and of metal armourings. Usually, asindicated on FIG. 1, which illustrates the simple case of a part withrectangular straight section, subject to a load P, it is considered thata part made of armoured concrete comprises, on either side of a neutralaxis x′x, two parts subject respectively to compression loads and totensile loads. The latter are absorbed by a layer of longitudinal bars Twhose cross-section is determined in relation to the loads applied and,in the case of a part subject to deflection, in relation to the distance(h) between the facing f1 of the compressed part and the centre ofgravity of the armourings in tension T.

[0005] Besides, it is necessary to provide as well, in the compressedsection, a layer of longitudinal bars that are linked with the bars intension by transverse armourings, called stirrups enabling, inparticular, to sustain shearing loads.

[0006] Generally, the reinforcement assembly of a concrete elementtherefore has the shape of a cage composed of two layers T, C oflongitudinal bars respectively active and passive, linked together bystirrups E.

[0007] Most often, bars of both armouring layers are superimposed inplanes parallel to the direction of the loads and spaced apart from oneanother, whereas the cage is thus composed of several parallel sectionslinked together by perpendicular joining bars whereas each sectioncomprises two bars or groups of bars connected by stirrups.

[0008] In order to maintain relatively low prices, the armouring barsare produced in very large quantities in specialised facilities thathave been arranged for manufacturing round bars of different sections,whereas the said bars can be twisted or corrugated for better adherence.

[0009] Going by catalogue, the user has only a limited number of typesof bars of different sections available and, in order to obtain thesection determined by calculation, it is often necessary to combine twoor three attached bars together.

[0010] Moreover, the official rules impose to leave a minimum encasingdistance between an armouring bar and the corresponding facing of thepart, to prevent the concrete from corroding and bursting. Consequently,the armourings must be placed accurately inside the moulded part, whiletaking into account the diameter of the stirrups surrounding the bars.

[0011] When concrete is moulded on site, the first operation consists inlaying formworks, called sheetings, which determine both facings of thewall and between which the reinforcing cage is mounted. Then, concreteis cast and it is necessary to wait for the concrete to set and hardenbefore removing the formworks and starting the next building step. Inthe case of a slab, the frame is placed on a formwork, then concrete iscast.

[0012] To simply the construction and to obtain, moreover, excellentsurface quality, it has been suggested for a long time to useprefabricated elements, realised in advance in a workshop especiallyfitted to that effect. Such a technique is valid, particularly, when alarge number of identical parts must be realised, for instance in thebuilding industry.

[0013] In this view, so-called heavy prefabrication techniques have beendeveloped in order, for example, to realise standardised facing andfloor elements. Indeed, for the construction of buildings, high capacitycranes are available, to install large dimension elements.

[0014] However, heavy prefabrication techniques have also been developedin civil engineering since mobile lifting vehicles are now available andenable to handle parts weighing several tons on the site.

[0015] For example, the inventor has developed, since 1981, an originaltechnique for constructing conduits buried under an embankment that mayprovide civil engineering works of certain consequence for road or railtraffic.

[0016] In this technique, described in particular in the European patentno 0.081.402, the conduit consists of juxtaposed rings comprising each,as a cross-section, two side elements forming abutment walls and anupper curved element forming a vault resting on the ends of the saidabutment walls.

[0017] If each ring is given a limited length, for example three meters,the corresponding elements can be placed on their longer side on a roadtrailer and be transported possibly over a long distance between theprefabrication works and the building site. Indeed, elements can bestandardised and it is then profitable to build a factory fitted withmoulds that can be used to realise a vast number of civil engineeringworks up to great distances away from the factory.

[0018] In all cases, for the armourings to work under the conditionsforeseen by calculations, the said armourings must be positionedaccurately inside the moulded part.

[0019] When parts are prefabricated in great numbers, the armourings areprepared in advance in specialised factories and delivered to theprefabrication workshop. The reinforcing cage of a prefabricated elementmust therefore exhibit sufficient rigidity in order to be handled andpositioned inside the formwork.

[0020] To ensure interconnection of the different sections of areinforcing cage, the longitudinal bars are generally bound withwire-ties or welded integral with the stirrups.

[0021] The realisation of reinforcing cages is therefore a ratherdelicate operation that must be performed by specialised staff, whichincreases the global cost of a prefabricated element, with respect tothe cost price of metal bars.

[0022] Besides the possibilities of realisation depend, obviously, onthe weight of the parts and on the lifting possibilities.

[0023] The technique for building buried elements described inparticular in the patent EP-0.081.402 enables to use parts that areparticularly thin with respect to their span. For example. thecapacities of mobile cranes that can be used currently on building yardsenable to handle upper elements with spans in excess of 10 meters.

[0024] Such a heavy prefabrication technique enables to carry outrapidly and cheaply civil engineering works of some importance, but therealisation and transport cost of the prefabricated elements plays asignificant role in the cost price of the civil engineering work.

[0025] The purpose of the invention, without putting into question thecalculation of the armouring and their general layout, consists inrealising a new type of reinforcing cage that enables, notably to reducethe cost of the prefabricated elements and to increase, for equalweight, the sizes of the parts that conventional lifting vehicles enableto handle.

[0026] The invention applies especially to the realisation of civilengineering works consisting of curved prefabricated elements describedin the previous patent EP-0.081.402. However, it has appeared that thereinforcing cages thus provided also exhibited advantages for othertypes of elements and, even, for on-site moulded concrete parts.

[0027] The invention therefore relates generally to a reinforcing cagefor an armoured concrete element with two facings spaced apart from oneanother on either side of a neutral axis, between which a reinforcingcage is imbedded, comprising at least two layers of longitudinalarmourings, respectively active and passive, substantially parallel,respectively to both facings and connected together by a transversearmouring, whereas each armouring has, as a cross-section, a determinedarea in relation to the loads to sustain in operation.

[0028] According to the invention, each longitudinal armouring consistsof a flat iron with rectangular section whose width and thickness aredetermined in order to provide the area necessary to provide thestrength required, with two plane faces, respectively an external faceturned toward the corresponding facing and an internal face turnedtoward the neutral axis, and the transverse linking armouring betweentwo opposite longitudinal armourings, respectively active and passive,consists of at least one elongated metal element, welded alternately onthe internal faces of both corresponding flat irons.

[0029] According to another particularly advantageous feature, thespacing between the flat irons forming the longitudinal armourings,respectively active and passive, is determined in relation to the loadsapplied and each facing is placed at a minimum encasing distance fromthe external face of the corresponding longitudinal flat iron, in orderto provide the concrete element with the thickness just necessary toprovide the strength required.

[0030] Such a reinforcing cage remains conventional in its design andcomprises therefore at least two armouring sections centred on planes atright angle to the facings and connected by joining bars. According tothe invention, each section comprises at least two longitudinal flatirons spaced from one another and connected together by joining barsconsisting of flat bands that cut the said longitudinal flat ironstransversely and that are welded to the internal faces of the latter.

[0031] In this preferred embodiment, the transverse armourings formaintaining the spacing comprise at least one undulated band, weldedalternately on the internal faces of both corresponding longitudinalflat irons of two layers, respectively active and passive.

[0032] In another embodiment, the transverse armouring comprises aseries of distinct elements, each composed of a portion of band with twobent ends welded respectively on the internal faces of both longitudinalflat irons.

[0033] The invention applies especially to the realisation of areinforcing cage for an element made of armoured concrete with twosubstantially parallel curved faces. In such a case, the longitudinalflat irons are curved so that their external faces are parallel,respectively to the corresponding facings of the element.

[0034] The invention also covers an element made of armoured concretefitted with such a reinforcing cage and comprising, in a known fashion,two regions, respectively active and passive, on either side of aneutral axis. Each longitudinal bar of the reinforcing cage is thencomposed of a flat iron with an external face parallel to thecorresponding facing of the element and spaced apart from the saidfacing by a minimum encasing distance (b). Thus, the thickness (H) ofthe element corresponding to the distance between the facings,respectively active and passive, can be limited to the value:

H=h+b+e/2

[0035] whereas (e) is the thickness of the active longitudinal flat ironand (h) the lever arm between the centre of gravity of the said flatiron and the passive facing of the element.

[0036] The invention also covers a method for realising a mouldedelement made of armoured concrete in which, in order to realise thelongitudinal armourings, flat bars with rectangular cross-section areused, whose width and thickness are determined in order to form the areanecessary to provide the strength required, whereas the said flat barsare positioned as foreseen for the armourings, respectively active andpassive, and connected together by a transverse armouring comprising atleast one band-shaped element, welded alternately on the internal faces,turned toward each other, of the said flat bars. The reinforcing cagethus formed is then placed in a mould delineating both facings whosespacing is determined in order to provide the thickness just necessaryto maintain a minimum encasing distance between the external face ofeach longitudinal armouring and the corresponding facing.

[0037] But the invention will be understood better with the followingdescription of certain particular embodiments given for exemplificationpurposes and represented on the appended drawings.

[0038]FIG. 1 is a principle diagram of the conventional embodiment of apart made of armoured concrete.

[0039]FIG. 2 is a detailed view at enlarged scale of FIG. 1.

[0040]FIG. 3 is a principle diagram of a part made of armoured concreteaccording to the invention.

[0041]FIG. 4 is a detailed view at enlarged scale of FIG. 3.

[0042]FIG. 5 is a partial view, in perspective, of a reinforcing cageaccording to the invention.

[0043]FIG. 6 shows, as a cross-sectional view, a reinforcing cage for aprefabricated curved element.

[0044]FIG. 7 is a partial cross-sectional view along the line I,I ofFIG. 6.

[0045]FIG. 8 shows an embodiment variation of the stirrups.

[0046] As indicated, FIG. 1 shows the conventional arrangement of thearmourings of a concrete element comprising two layers of longitudinalbars C, T, linked by stirrups E. It is known that, usually, the stirrupsE are composed of wires with significant diameter, revolving aroundlongitudinal bars ad indicated on FIG. 2, which is a detailed view, atenlarged scale, of FIG. 1.

[0047] Since metal armourings must be maintained away from thecorresponding facing by a minimum encasing thickness (b), the distancebetween the centre of gravity of a longitudinal bar and thecorresponding facing is therefore:

a1=D/2+d+b

[0048] whereas D is the diameter of the armouring, d the diameter of thestirrup and b the minimum encasing thickness.

[0049] Still it is known that, in the case for instance of a partsubject to bending, it is the lever arm (h), i.e. the distance betweenthe centre of gravity of the armourings in tension and the compressedfacing, that plays a part in calculating the strength. The externallayer of concrete, along the facing, is used solely for the protectionof armourings. The inventor therefore had the idea of reducing thethickness of this external layer in order to reduce the overallthickness H of the element and, consequently, its weight and thequantity of concrete to use.

[0050] To this end, the ideas generally admitted for the realisation ofreinforcing cages had to be put into question.

[0051] Indeed, whereas until now it had appeared normal and, even,inevitable to use concrete round irons that can be found usually incommerce, the inventor realised that the recent evolution of themetallurgical techniques had lowered the prices of flat irons and thatthe cross section necessary to provide the strength required could beobtained by resorting to thin flat irons connected by bands welded tothe opposed internal faces, so that the global thickness of the cageand, consequently, that of the concrete element, can be reducedsignificantly.

[0052]FIG. 3, which is a principle diagram analogous to that on FIG. 1,shows a reinforcement element according to the invention in the case ofa concrete element 1 with rectangular section having two facings,respectively a stressed face 11 and a compressed face 12. As indicated,each layer of longitudinal armourings comprises at least one flat iron 3having a rectangular cross section whose area is calculated as for eachround bar (T) of FIG. 1.

[0053] Similarly, the passive bars (C) of FIG. 1 are replaced with flatirons 3′.

[0054] Besides, the stirrups consist of thin bands welded to the faces31, 31′ of the longitudinal flat irons 3, 3′ turned to the inside of thepart.

[0055] In a particularly advantageous fashion, each stirrup 4 may becomposed of an undulated band whose apexes touch, alternately, theinternal faces 31, 1′ of two flat irons 3, 3′ and are welded to the saidfaces, as represented on FIG. 5.

[0056] As usual, the reinforcing cage 2 is composed of several sections21, 22 . . . centred on parallel planes (P1, P2 . . . ) at right angleto the neutral axis 10 of the part 1. These different sections areconnected together by joining bars parallel to the neutral axis 10,which are advantageously composed of flat bars 5, 5′ welded respectivelyon the internal faces 31, 31′ respectively of both longitudinal flatirons 3, 3′. These flat bars 5, 5′ pass between the apexes of theundulated band 4, which are welded to the same internal faces 31, 31′.

[0057] In a reinforcing cage thus realised, the stirrups 4 extendtherefore solely between the internal faces of the longitudinal flatirons and, as shown on FIG. 4, the distance between the external face32, 32′ of each longitudinal flat iron 3,3′ and the corresponding facing11, 12 of the part 1 must consequently be only equal to the minimumencasing distance (b).

[0058] The distance (a2) between the centre of gravity of the stressedbars 3 with thickness (e) and the corresponding facing 11 is thus:

a2=b+e/2

[0059] If this arrangement is compared to that of FIG. 2, it appearsthat this distance a2 is smaller than the previous distance a1 since thethickness (d) of the stirrups E is suppressed and that the thickness (e)of a flat iron 3 is smaller than the diameter D of a round bar with thesame transverse area.

[0060] For a same lever arm (h) corresponding to the loads applied, thetotal height of the part,

H2=h+a2

[0061] is thus reduced.

[0062] For exemplification purposes, as the minimum encasing distance is30 mm, if we replace a round bar with a diameter of 14 mm associatedwith stirrups made of 8 mm wires, with a flat iron of equivalent section25×6, the distance a1 was 45 mm in the conventional layout and thedistance a2 will be only 30 mm in the layout according to the invention.

[0063] For a same lever arm 4 between the axis of the stressed bars andthe compressed facing, the thickness of the girder is therefore reducedby 15 mm with equal strength.

[0064] Obviously, it also suffices to leave a minimum encasing distance(b) between the upper faces 32′ of the compressed bars 3′ and thecorresponding facing 12 of the part.

[0065] The thickness of concrete can then be reduced at each facing.

[0066] It should be noted that the reduction in thickness of the elementis proportionally more sensitive for parts already having quite a smallthickness with respect to their span as in the case of curved elementsused to realise the upper portion of a buried conduit according to thetechnique described in the patent EP-0.081.402.

[0067] A reduction, for instance of 20 mm, in the thickness of eachprefabricated element can thus be reflected by significant savings, evenfor the realisation of a single work.

[0068] Generally speaking, the invention thus does not put into questionthe design and the calculation of the reinforcing cage, whereas thepositioning and the sizes, as a cross section, of the armourings aredetermined conventionally by applying the usual methods of calculation,taking into account the profile of the concrete part to be realised aswell as the loads applied.

[0069] It should be noted, however, that the use of metallic flat barsas main armourings enables to realise reinforcing cages of quite variedshapes, whereas such flat bars can be shaped easily and, possibly,mass-produced.

[0070] For example, to improve the anchoring effect in concrete, theends of the longitudinal bars are usually curved into crossheads whosecurvature radius depends on the diameter of the bar.

[0071] The flat irons used, according to the invention, to realise thearmouring bars can easily be folded back at their ends, while keepingthe same ratio between the curvature radius of the crosshead thus formedand the thickness of the flat iron. As this thickness is smaller thanthe diameter of an equivalent round bar, the space requirements of thecrosshead will be reduced, which may make the realisation of the cageeasier.

[0072] Similarly, the metal bands 4 forming the linking stirrups betweenthe longitudinal flat irons 3, 3′ can be formed easily, for example, inorder to sustain the shearing loads as efficiently as possible.

[0073] Besides, taking into account the relatively small thickness ofthe flat irons used, the said flat irons can be delivered to themanufacturing workshop of the armourings in the form of reels, whereasthe flat irons are simply unwound and straightened on site according tothe requirements.

[0074] Besides, a reinforcing cage according to the invention ismanufactured more easily than a conventional cage.

[0075] Indeed, in the conventional technique, there are onlyquasi-punctual contacts between the round bars and the stirrups. Thelinks between the different elements to form an integral assembly aremade either by wire-ties or, point-by-point, by arc welding and theseoperations are rather long and costly.

[0076] In the case of the invention, conversely, the different elementsof the reinforcement are all composed of flat bands whose opposite facesare applied on one another and can be welded easily, for example withpliers. The realisation of a reinforcing cage is therefore easier andcalls for less specialised staff. It is thus possible to reduce not onlythe quantity of concrete to use, but also the manufacturing cost of thereinforcing cage and the global cost of a prefabricated elementaccording to the invention can thus be reduced significantly.

[0077] The advantages supplied by the invention compensate thereforeeasily the price increase of the rods used in a frame according to theinvention, with respect to a conventional frame composed of round bars.

[0078] Besides, if the concrete round irons form a mass product whoseprice is relatively low, there are only standardised products availableon the market. After having determined the required steel section toabsorb the loads applied, it is thus necessary, in the design of thereinforcement, to take into account sections of bars that can be placedby combining, for instance, several bars in order to obtain therequested cross section.

[0079] In the case of the invention where metallic flat iron are used,which can be obtained cheaply, for example by splitting sheet metals, itis possible to procure flat irons whose area, in straight section,corresponds exactly to the steel section determined by calculation andthe realisation of a cage is easier.

[0080] Moreover, the invention benefits from continuous evolution of themanufacturing techniques of the sheet metals that have enabled to reducethe manufacturing costs considerably and, besides, to obtain a very widevariety of products having quite diverse structural features.

[0081] In particular, it is now possible to realise economically steelsheets with high elastic limit and the use of flat irons obtained fromsuch sheets will enable to reduce, with equal strength, the quantity ofsteel necessary to reinforcement. Besides, it is also possible to usesteels having an elastic limit perfectly suited to the features of theconcrete and, thus, to reduce the risks of cracking.

[0082] Moreover, we know that the concrete round irons are particularlysensitive to the risks of corrosion, which justifies a relatively greatencasing thickness. The advantages supplied by the invention, enableconversely, to contemplate the use of steels that resist to corrosionbetter, which would allow reducing the necessary encasing thicknessstill further and, consequently, the global thickness of the concreteelement.

[0083] Besides, the expression “flat iron” used in the presentdescription, corresponds to the usual vocabulary but, according to theinvention, any type of flat bar having the required strength can be usedas reinforcement.

[0084] It should be noted, moreover, that for the same cross section,the perimeter of a rectangular flat iron is larger than that of a roundbar. The invention enables therefore to improve the adherence betweenthe armourings and the concrete.

[0085] Anyway, to improve adherence, it can be contemplated whenmanufacturing the flat irons, to realise corrugated portions, as forconcrete rounds.

[0086] Besides, the flat irons constituting the armourings or the metalsheet from which they are formed, can be subject to a surface treatmentenabling to improve corrosion strength and/or adherence.

[0087] As indicated, the invention applies especially to the realisationof curved prefabricated elements used, for example, to constitute thevault of a passageway buried under an embankment.

[0088] As described in the patent EP-0.081.402, such an elementrepresented as a cross section on FIG. 6, comprises two curved facings,respectively a concave intrados face 61 and a convex extrados face 62that have a cylindrical shape with generatrices parallel to alongitudinal axis of the element, perpendicular to the plane of thefigure.

[0089] Advantageously, each end 63 of the element exhibits a convexrounded face liable to engage into a concave groove of an abutment wallelement, in order to constitute an articulated bearing.

[0090] As usual, the reinforcing cage is composed of several parallelsections 60, distributed over the length of the element 6 and connectedtogether by joining bars 5, 5′.

[0091] According to the invention, each reinforcing section 60 comprisestwo longitudinal rods 3, 3′ each composed of a flat iron that, in thecase of reinforcing a curved element 6 is curved in itself so that,after installation, each flat iron 3, 3′ is parallel to thecorresponding facing 61, 62.

[0092] In each section 60, both flat irons 3, 3′ are connected togetherby an undulated metal band 4, maintaining the space between them.

[0093] As shown on FIG. 5, the undulated bands 4 forming the stirrups oftwo successive sections can advantageously be staggered longitudinallywith respect to one another in order to facilitate the penetration ofconcrete between the various elements of the cage.

[0094] The rounded end 63 of the element 6 can be armoured, simply, by alongitudinal rod 64 with flat or round section connected to both layersof the cage by rods or bands 65 welded to the ends, respectively, of twolongitudinal flat irons 3, 3′ of each section of the cage.

[0095] Obviously, the invention is not limited to the details ofembodiment that have just been described for exemplification purposes,but also covers the variations still within the protection frameworkdefined by the claims.

[0096] For example, the linking stirrups between two reinforcementlayers could be made of distinct elements composed of portions of bands41 with bent ends 42, 42′ welded respectively on both flat irons 3, 3′of each section of the cage, as represented on FIG. 8. The space betweenthese elements 41 as well as their tilting angle (A) with respect to theflat irons 3, 3′ could also vary in relation to the position of thestirrup in the element and to the calculation of the loads applied.

[0097] Besides, we have described the invention in its application tothe manufacture of curved elements for the realisation of buriedpassageways of the type described in the patent EP-0.081.402 that enableto use particularly thin elements with respect to their span. But theinvention could also apply to other types of elements such as girders orslabs.

[0098] Similarly, if the invention has been developed for therealisation of prefabricated elements, the use of the reinforcing cageof such type would also exhibit advantages in the case of concrete partsmoulded on site.

[0099] The reference signs inserted after the technical featuresmentioned in the claims solely aim at facilitating the understanding ofthe said and do not limit their extent whatsoever.

1. A reinforcing cage for an armoured concrete element (1) with twofacings spaced apart from one another on either side of a neutral axis(10), between which a reinforcing cage (2) is imbedded, comprising atleast two longitudinal armourings, respectively active (T) and passive(C), substantially parallel, respectively to both facings and connectedtogether by a transverse armouring (E), whereas each armouring has, as across-section, a determined area in relation to the loads to sustain inoperation, characterised in that each longitudinal armouring consists ofa flat bar (3, 3′) with rectangular section whose width (I) andthickness (e) are determined in order to provide the area necessary toprovide the strength required, with two plane faces, respectively anexternal face (32) turned toward the corresponding facing (11, 12) andan internal face (31) turned toward the neutral axis, and in that thetransverse linking armouring between two opposite longitudinalarmourings, respectively active (3) and passive (3′), consists of atleast one elongated metal element (4), welded alternately on theinternal faces of both corresponding flat bars (3, 3′).
 2. A reinforcingcage according to claim 1, characterised in that the spacing between theflat bars forming the longitudinal armourings, respectively active (3)and passive (4), is determined in relation to the loads applied and inthat each facing (11, 12) is placed at a minimum encasing distance (b)from the external face (32) of the corresponding longitudinal bar (3,3′), in order to provide the concrete element (1) with the thicknessjust necessary to provide the strength required.
 3. A reinforcing cageaccording to one of the claims 1 and 2, characterised in that itcomprises at least two armouring sections (21, 22) centred on planes (P)at right-angle to the facings (11, 12) of the element (1) and connectedby joining bars (5), whereas each section (21, 22) comprises at leasttwo longitudinal flat bars (3, 3′) spaced from one another and wherebythe joining bars (5) consist of metal bands transverse to the saidlongitudinal flat bars (3, 3′) and welded to the internal faces (31,31′) of the said flat bars.
 4. A reinforcing cage according to one ofthe previous claims, characterized in that the transverse linkingarmouring between two longitudinal flat bars (3, 3′) comprises at leastone undulated band (4), welded alternately on the internal faces (31,31′) of the said flat bars.
 5. A reinforcing cage according to one ofthe claims 1 to 31 characterised in that the transverse linkingarmouring between two longitudinal flat bars (3, 3′) comprises a seriesof distinct elements (41), each composed of a portion of band with twobent ends (42, 42′) welded respectively on the internal faces (31, 31′)of both longitudinal flat bars (3, 3′).
 6. A reinforcing cage accordingto one of the claims 3, 4, 5, characterised in that, the element made ofarmoured concrete (1) having two substantially cylindrical curved faces(11, 12), the longitudinal flat bars (3, 3′) of each armouring section(21, 22) are curved so that their external faces are parallel,respectively to the corresponding facings (11, 12) of the element (1).7. An element made of moulded armoured concrete, comprising areinforcing cage (2) imbedded between two facings (11, 12) spaced fromone another, characterised in that the reinforcing cage (2) is realisedaccording to one of the previous claims.
 8. An element made of armouredconcrete according to claim 7 comprising two facings, respectivelyactive (11) and passive (12), on either side of a neutral axis (10) anda reinforcing cage (2) comprising at least one active longitudinal bar,characterised in that each active longitudinal bar is composed of a flatiron (3) with an external face (32) parallel to the active facing (11)and in that the thickness (H) of the element corresponding to thedistance between the facings, respectively active (11) and passive (12),is equal to: H=h+b+e/2whereas h is the distance, calculated in relationto the loads applied between the passive facing (12) and the centre ofgravity of the active longitudinal flat bar (3), b is a minimum encasingdistance between the external face (32) of the longitudinal flat bar (3)and the active facing (11) of the element (1) and (e) is the thicknessof the longitudinal flat bar (3).
 9. A method of realisation of anelement made of moulded armoured concrete with two facings (11, 12)spaced apart from one another, between which a reinforcing cage (2) isimbedded, comprising at least two longitudinal armourings, (T, C),substantially parallel, respectively to both facings (11, 12) andconnected together by a transverse armouring (E), a method in which thepositioning of the longitudinal armourings, respectively active (3) andpassive (3′), on either side of a neutral axis (10), their area in crosssection, and the profile of the transverse armourings are firstlydetermined in relation to the loads to sustain, such a reinforcing cageis built, then placed in a form delineating the facings (11, 12),concrete is cast and, after setting, the element thus realised isremoved from the form, characterised in that, in order to realise thelongitudinal armourings, metal flat bars (3, 3′) with rectangularsection are used, with width (I) and thickness (e) determined in orderto form the area necessary to provide the strength required, whereas thesaid flat bars (3, 3′) are positioned as foreseen for the armourings,respectively active and passive, and connected together by a transversearmouring (4) comprising at least one element welded alternately on theinternal faces (31, 31′), turned toward each other, of the said flatbars (3, 3′), whereas the reinforcing cage (2) thus formed is thenplaced in a mould delineating the facings (11, 12) whose spacing isdetermined in order to confer the moulded element the thickness justnecessary to maintain a minimum encasing distance (b) between theexternal face (32, 32′) of each longitudinal flat bar (3, 3′) and thecorresponding facing (11, 12).